Abstract:The expression characteristics of a class of pathogenesis-related protein (PR) genes, namely basic chitinase, β-1, 3-glucanase, osmotin and extensin, were studied in tobacco (Nicotiana tabacum cv. Wisconsin 38) plants. RNA blot hybridization showed that these four genes were regulated in a developmental and organ-specific manner in tobacco. In the transgenic fascicular shoots which contained the active cytokinin biosynthetic gene (ipt gene) from Agrobacterium tumefaciens, the expressions of these four genes were co-regulated by overproduction of endogenous cytokinins and vector effect. Cytokinins reduced the expressions while vector effect induced the expressions of these four genes. Heat shock also de creased the steady-state levels of the four RNAs. These data suggest a complex regulation of PR genes.